The present invention relates to a system and method of simulating a steering resistance torque on a vehicle steering wheel of a steer-by-wire system using a magnetorheological device and a motor.
Vehicle steer-by-wire systems are known and are ever so changing. Steer-by-wire systems eliminate the mechanical linkages between the steering wheel and the vehicle road wheels and allow for electronic steering of the vehicle by a driver thereof. Thus, in order to provide an appropriate feel to a steer-by-wire system, mechanisms are placed adjacent the steering wheel and steering shaft of the vehicle to generate resistive torque which resist a driver when the steering wheel is rotated for a vehicle turn during normal operation of the vehicle. This simulates for the driver an appropriate feel to the vehicle steering wheel as though the driver were driving a vehicle having a conventional mechanical steering wheel assembly.
Although current systems and methods of providing steering resistive torque are adequate, improvements can be made thereto. Typically, a motor is placed on the steering wheel shaft to generate torque applied on the steering wheel. This accomplishes a resistive torque on the steering wheel when the driver rotates the steering wheel during a turn. Torque generated by the motor has been identified as xe2x80x9cactivexe2x80x9d force or torque on the steering wheel, since such torque is generated with a direction opposite the direction in which the driver rotates the steering wheel. The power required to generate such torque is relatively significant. However, manufacturers have been challenged in improving current systems and methods, specifically in areas of response time and power efficiency.
Thus, it is one aspect of the present invention to provide a system and method of simulating a steering resistance torque on a vehicle steering wheel of a steer-by-wire system.
It is another aspect of the present invention to provide a system and method of simulating a steering resistance torque for improved response time and power efficiency. In this aspect, the present invention provides an improved steer-by-wire system which responds in less time to actual steering wheel and vehicle parameters and operates with improved power efficiency. The present invention includes a steer-by-wire system which uses a motor and a magnetorheological (MR) device for variable damping on the steering wheel.
In this aspect of the present invention, implementation of both the motor and the MR device allows the system to generate an improved torque response, saving time and energy, depending on steering wheel and vehicle parameters. As mentioned above, torque generated by the motor has been identified as xe2x80x9cactivexe2x80x9d force or torque on the steering wheel, since such torque can be generated in either rotational direction of the steering wheel. Generally, xe2x80x9cactivexe2x80x9d torque is applied in a direction opposite the direction in which the driver rotates the steering wheel. However, torque generated by the MR device has been labeled as xe2x80x9cpassivexe2x80x9d force or torque on the steering wheel, since such torque is generated with constant resistance that may react only in the opposite direction in which the steering wheel is rotated. Based on vehicle and steering wheel parameters, the system may determine whether active torque, passive torque, or a combination thereof will be applied on the steering wheel. The extent to which passive force is used instead of active force improves the power efficiency of the steering system because the magnetorheological device produces more torque than the motor, given the same amount of electrical energy.